Silicate coatings



3,372,938 Patented Mar. 5, 1968 [ice 3,372,038 SILICATE COATINGS HelmutHans Wilhelm Weldes, Havel-town, and David I. Netting, Swarthmore, Pa.,assignors to Philadelphia Quartz Company, Philadelphia, Pa, acorporation of Pennsylvania No Drawing. Cntinuation-in-part ofapplication Ser. No. 311,215, Sept. 24, 1963. This application Aug. 18,1964, Ser. No. 390,447

9 Claims. (Cl. 1061) This application is a continuation-in-part ofapplication Ser. No. 311,215 filed Sept. 24, 1963, now Patent No.3,345,194.

This invention relates to the preparation of corrosionresistant coatingson metal and comprises the preparation of coatings having powderedmetals, such as Zn, Al, Pb, Ti, Fe and their alloys, dispersed in anaqueous vehicle of an organic ammonium silicate.

The coating compositions of this invention are adapted to be applied tometal surfaces by spraying, dipping, brushing, roll-coating or the likeand may be air-dried or baked at suitable temperatures to produce ahard, flexible, tenacious coating film which is resistant to abrasionand protects the substrate from corrosion.

BACKGROUND In the known aqueous systems of the prior art designed forthe preparation of corrosion-resistant coatings the Water soluble orwater dispersible binder may be an aqueous latex, an alkali metalsilicate, an organic silicate ester, a colloidal silica sol, or thelike; the coating compositions being applied to metal surfaces and thentreated to produce a protective film thereon. While such coatingcompositions containing finely divided metals provide useful protectivecoatings for metallic surfaces, various drawbacks have been noted. Thecompositions of the alkali metal siilcate must be carefully controlledsince the use of highly concentrated alkali metal silicate solutions maycause a reaction to take place with evolution of gases. This results inthe formation of blisters in the coating film which is, of course,undesirable. These binders also re quire post-cure applications, such asthe use of phosphoric acid as a secondary application.

If the self-curing additives, such as lithium compounds and boric oxide,etc. are used, the coatings are inferior in the degree of insolubility,are slow drying and slow curing. The organic orthosilicate ester binderstend to form a rather soft coating which is not sufficientlyabrasionresistant. These corrosion-resistant coatings of the prior artalso require a very carefully prepared metal surface, and sand blastingto a White metal surface is almost always necessary. Furthermore, thefree metallic zinc in the coatings is likely to cause undesirablereactions in contact with gasoline and to effloresce on contact with seawater.

The preparation of corrosion-resistant inorganic coatings on metal bythe use of aqueous alkali metal silicate solutions with finely dividedmeta-l providers dispersed therein is well-known. The early art isreviewed by James G. Vail in Soluble Silicates, volume II, ReinholdPublishing Co., New York (1952) pages 283-284. More recent patentsinclude Munger et a1. 2,998,323; Drummond 2,765,237 and MacMahon3,130,061..

The development of our invention will be described in terms of the useof metallic zinc, although it will be recognized that in general theseconditions apply to all metallic powders. The zinc-rich,corrosion-resistant metal coatings of the prior art have suffered fromcertain insufiiciencies:

(a) The paint prepared for application to the surface is quite reactiveand has a very short pot life of less than 24 hours;

(b) The paint therefore has to be mixed immediately prior to use;

(c) The paint components have to be sold in multiple containers andapplication involves from two to four, or even more, steps;

(d) In many such systems the coating has to be set by application of asecond coating of a reactant material;

(e) Where the coatings are self-hardening or self-curing they must beapplied quickly and the setting or hardening process is usually slow.

In our copending application, Ser. No. 311,215, of which this is acontinuation-in-part, we have disclosed a new aqueous binder system forcoatings which is both organic and inorganic and may be described as anorganic ammonium silicate. In that application we disclose the effect ofadding PbO in forming hard scratch-resistant coatings, the specialapplicability of alkyltriethanola-mmonium silicates as binders forcoatings on metals, and the addition of metallic zinc to these coatingsto promote resistance to corrosion of metal substrates, especially thecorrosion of ferrous substrates.

OUR INVENTION We have found now not only that corrosion resistant,insoluble, air-curing coatings from aqueous systems can be formed usingorganic ammonium silicates and PhD with metallic powder, such as zincmetal powder, for example, but that even without the presence of thelead oxide strongly adherent, insoluble, air-curing, corrosion-resistantcoatings can be obtained when the metallic powder is present, and thatin the presence of lead oxide these combinations of organic ammoniumsilicates and metal powders have a greatly extended pot life of sevendays or more. Furthermore, we have found that if dry powders of thecomponents are mixed together, they may be stored for long periodswithout deterioration, and after dispersion with water have a furtherlong, useful pot life for hard, flexible, tenacious, self-curingcoatings which are resistant to corrosion over pH ranges normal for suchcompositions. This has obvious commercial economies in the reduction offreight costs, ease of handling and application, etc.

PROPERTIES OF THE COATING These corrosion-resistant coatings of ourinvention require less preparation of the surface, become hard andwater-resistant immediately on drying and furthermore are self-curing.Thus the labor costs are distinctly lower since less surface preparationis required and much less time is required for application. In thecompositions of the prior art, it is not uncommon to sell kits of threeor more units for the preparation of the total coat. Furthermore, theoverall costs of the raw materials for our compositions are reduced, andour coatings have improved adhesion with thin coatings, highflexibility, and extreme hardness. The zinc apparently interacts withand is protected by the binder and does not thereafter deleteriouslyatfect gasoline or interact with water on immersion.

When heated at high temperatures, the organic portion of the silicateburns off, leaving the silicate which reacts with the metal powderforming a hard, corrosion and abrasion resistant coating of metalsilicate. These coatings are exceptionally stable and have long, usefullives, even at high temperatures.

Thus the coatings of our invention are hard, strongly adherent andcorrosion-resistant on metal. They withstand extremes of Weather andnatural environments, such as sea water, and may be used on the holdsand hulls of ships, missile towers, refinery equipment, boiler stacks,-

gasoline engine manifolds, and similar surfaces exposed to corrosiveconditions and/or high temperatures without deterioration of theirweather-resistant properties.

A measure of the stability of the aqueous formulation is the time whichelapses until the first measurable amount of hydrogen is produced by thereaction of the binder and the metallic zinc. With alkali metalsilicates this time is from 1 to 24 hours. Mixtures of the organicammonium silicate binders containing metallic zinc pigments were madewith 20 ml. of the aqueous organic ammonium silicate (12.50 SiO:methyltriethanolammonium ion-)at 32% of SiO 1.5 grams of PhD (18.5%based on the silica), and 60 grams of powdered zinc. The containers wereclosed and any gases produced were collected in tubes. The followingtable shows the age of the mixtures when gas started to form. A total ofabout 100 ml. of gas was released from each mixture:

First gas Zinc dust: formation, days High efliciency 25 #111 18 THEORGANIC AMMONIUM SILICATE The organic ammonium silicates arefundamentally inorganic silicates. Thus their reactions arecharacteristic of electrostatic bonds rather than of the covalent bondsof the organic silicate esters, such as ethyl orthosilicate. Since theseorganic ammonium silicates are alkali silicates, rather than silicasols, they react readily with metals and metal salts which accounts fortheir ability to set rapidly and form very insoluble adherent coatingswith metals and other hydrophilic surfaces. The volatility and/ orinstability of the cation of organic substituted ammonium at relativelylow temperatures after reaction of the silicate ion accounts for thehigh thermal stability and strength characteristics of the residual filmafter heating to high temperatures. There is no fiuxing alkali cationremaining in the coating.

We prefer to use organic ammonium silicates that can be characterized bythe formula:

X (N R O -YSiO ZH O wherein:

N represents a nitrogen atom; n is a small integer less than andpreferably less than 5; X, Y and Z represent numbers defining therelative amounts of each of the component parts of the compound.Specifically, X is 1, Y is preferably between 0.5 and 50, and Z ispreferably between 0 and 99; R represents alkyl radicals containingbetween about 1 and carbon atoms, at least one of which is an omegahydroxy alkyl group (preferably one or more of these R groups areethanol groups and especially preferred are the alkyl ethanolcombinations); up to four R groups are associated with each N;

p is at least 4, indicating total bonds of R groups to N; and

s is an integer from 1 to p, indicating the number of different types ofR groups.

In a more specific sense, it is believed that the organic ammoniumsilicate settable components useful in connection with this inventioncan be characterized by the formula:

wherein N, X, Y and Z have the significances noted above and R R R and Rrepresent alkanol radicals containing between about 1 and 20 carbonatoms.

Preferred specific examples of organic ammonium silicates useful inaccordance with this invention would include (a) sodium-freetetraethanolammonium silicate, (b) N,N,N-tris-(B-hydroxyethyl)-N'-[tris(,8 hydroxyethyl) ethylammonium] piperaz'inium silicate, (0) diethanolmorpholinium silicate, (d) hexaethanolethylene diammonium silicate, (e)methyl triethanolarnmonium silicate, (f) dimethyl diethanolammoniumsilicate, (g) ethyl triethanolammonium silicate. We prefer those corn=pounds described in our copending application, Ser. No. 311,215, withratios of silica to organic ammonium ion of between 4.5 and 13.0, asabove a ratio of 13.0 the zinc dust can be rubbed off of a dry coatingand the whole coating can be easily rubbed off after soaking in waterfor one hour. Similar coatings made with the ordinary commercial silicasols also may be easily rubber away after soaking. On the other hand,ratios more alkaline than 4.48 do not dry out. A ratio of 4.48 providesa coating which is somewhat softer than normal and, therefore, isapproximately the lower limit. Coatings prepared with thealkylethanolammonium silicates are somewhat harder and have a betteradhesion than coatings prepared with the tetraethanolammonium silicatesand, therefore, we prefer to use the alkylethanolammonium silicates,such as methyltriethanolammonium silicate.

As these organic silicates react with soluble calcium salts, zinc metalpowders with additives such as CaO will not make satisfactory coatings.The particle size of the zinc will determine the smoothness of thefinished surface and affect the viscosity of the overall system. Inpreparing these formulations, it is important to balance the SiO contentof the binder. Too high a concentration may lead to crazing of the filmwhile too low a concentration will not leave sufficient silicate to holdthe pigment in place. We have found, as shown in our parent application,that the optimum content of SiO in the binder system will fall at about32% SiO more or less.

ADDITIVES A thickening and gelling agent is generally useful. We preferhydrous siliceous fillers which generally are nonreactive but willincrease the consistency of the mix and, in particular, we have foundthat hydrous magnesium silicates, such as Ben-A-Gel, sold by NationalLead Co., are particularly effective. The use of a thickening agentdevelops the best paint consistency characteristics, forming paintswhich leave smooth, continuous films and do not run or sag. We havefound, however, that it is better not to try to add the thickening agentdirectly but, rather, to prepare an aqueous suspension of the thickenerand then to add this suspension to the rest of the vehicle or binder.With hydrated magnesium silicate, for instance, we have found that theaddition of 0.32 to 0.66% based on the silica present in the binder willincrease the adhesion from an initial figure of 400 g. to a figure Of600 g. as determined with the Hoffman Scratch-Hardness Tester.

The addition of lead oxide, or equivalent materials, is described in ourparent application. In the metallic pigmented paints, such as thezinc-rich coatings, based on our organic ammonium silicates, the leadoxide is not necessary and, in fact, decreases the water-resistance ofthe coating. Coatings of tetraethanolammonium silicate binders withratios between approximately 9 and 13 cannot be rubbed off after soakingfor one hour in water, but coatings made from the same silicate with theaddition of 18.5% of lead oxide based on silica can be rubbed off themetal substrate after soaking for an hour in water. The addition of leadoxide does not have as great an effect on the alkyltriethanolammoniumsilicate binders as on the tetraethanolammonium silicate binders, andcoatings containing 18.5% of lead oxide with themethyltriethanolammonium silicates in a ratio range from 9.7 to 12.5cannot be rubbed off after soaking for one hour in water. On the otherhand, silica sols or higher ratio tetraethanolammonium silicates, suchas 22.5, as well as lower ratios, such as 4.5 or below, all gell in theball mill while lead oxide is being ground into the mixture. They arethus much too reactive with the lead oxide.

On the other hand, we have found that while the addition of lead oxideto the metal powder-rich coating compositions decreases thewater-resistance of the coating, it greatly increases the pot life ofthe paint. With no lead oxide in the paint, 24 hours is the averageuseful life; while with 18.5% PbO, based on the SiO ground into thesilicate vehicle the average useful life of the paint is at least 7days. We have further found that this useful life is maintained evenafter excess PhD is removed from the binder solution.

As indicated above, the use of multiple coatings is a regular practicein the industry. We have found that as a base vehicle our zinc-richcoatings of this invention are very effective. They may be covered witha lead oxide coating of our parent application and an organic basevehicle coating may be applied over the lead oxide coating or in placeof it.

It is, of course, possible to include inorganicextenders, such as redlead, zinc oxide, iron oxide, aluminum oxide, etc. and inorganicpigments such as iron oxide, titanium oxide and the like. Mica,bentonite, and the like, may be used to increase flexibility in thecoating.

It is also well-known to prepare Waterproof cements using large amountsof lead oxide with small amounts of glycerine. In our systems it wasfound that in the organic ammonium silicate systems glycerine did notappear to react with the lead oxide but did appear to react with thelead oxide in the commercial silica sol systems. In general, smallamounts of glycerine increased the drying time of the coatings andlarger amounts increased the water solubility of the coatings.

THE EXAMPLES The following examples are given for the purpose ofillustrating the invention and include the best mode contemplated by theinventors for carrying out their invention. They are not to be construedas limiting the invention which is defined in the claims. As indicatedabove, the use of metallic powders has been developed with metallic zincpowders as exemplary compositions.

In the examples we have used the following materials.

Organic ammonium silicates (indicated in tables as OAS)1-Tetraethauolammonium ion: 22.5 SiO 5-Tetraethanolammonium ion: 13.05Si0 4Tetraethanolammonium ion: 9.69 SiO 3Tetraethanolammonium ion: 4.48SiO 610-Tetraethanolammonium ion: 1.89 SiO 220-Methyltriethanolammoniumion: 12.5 222Methyltriethanolammonium ion: 9.54

Zinc dusts #AAl-From General Smelting Co.average particle size 9 micronswith 97.5% through 325 mesh. This is 97.0% metallic zinc, 2.85% zincoxide and 0.1% Pb.

Asarco #1-Arnerican Smelting & Refining Co.particle size of about 8microns with 97% through 325 mesh. It is 97.0% zinc, 2.5% zinc oxide,0.2% Pb, and 0.2% Fe.

Asarco high efficiencyHas an average particle size of 3.8 to 4.5 micronswith 99% through 325 mesh. It is 96.0% metallic zinc, and 2.9% zincoxide.

Asarco LD Ill-Comparable to Asarco #1, and has about 97.5 to 98%metallic zinc with 2.0% zinc oxide, and an average particle size of 5.5to 7.5 microns...

All samples of metallic zinc containing CaO as a gas-, sing retardantwere found to react with the silicate within minutes and, therefore, arenot satisfactory for use with organic ammonium silicate vehicles.

Ben-A-Gel is a hydrous magnesium silicate sold by National Lead 00. Leadoxide, li-tharge C.P., was obtained from J. T. Baker Chemical Co. as wasthe manganese dioxide. USP talc was obtained from Merck & Co. Inc., andTiO (titanium dioxide) known as R-610 was obtained from Du Pont Co.

The tests were carried out on Q-Panel iron strips obtained from theQ-Panel Co. These are cold-rolled steel panels four inches by eightinches in size with a simulated sand blasted surface on one side. i

In general, we have found that the best results were obtained with 55 to70 grams of metallic zinc dust per 20 ml. of an organic ammoniumsilicate containing 32% SiO for example. With 75 to grams of zinc dustthe coating tend-ed to be soft and some zinc dust could be rubbed off.With 55 to 70 grams of zinc powder there was good hardness and completeone-coat coverage. With 40 to 55 grams of zinc dust the coating is hardbut the coverage is poor and, in general, two coats are necessary forcomplete hiding of the metal surface.

In the following tests the paints were prepared by mixing in theproportion of 65 grams of zinc powder to 20 ml. of an organic ammoniumsilicate solution with 32% of SiO The zinc dust was added slowly to theorganic ammonium silicate binder with constant stirring. While thiscomposition may be used directly as a paint, it needs frequent stirring.If the silicate in the paint is increased in concentration, oradditional zinc dust is added to thicken the paint, the coating tends tocrack and the adhesion to the metal is decreased. We have found that thesystem may be thickened with other fillers and that a hydrous magnesiumsilicate filler is especially helpful.

When using a filler such as hydrous magnesium silicate, a preferredmethod of preparation is as follows. The organic ammonium silicate isused at a concentration of 45% SiO If lead oxide is to be included, 0.98lb. of PbO is then milled into each gallon of the organic ammoniumsiilcate until completely dispersed. A pebble mill or a ball mill may beused. This gives 18.5% by weight of PhD based on the content of SiO Themixture of lead oxide and binder is then diluted with water which hasbeen thickened with 2.6% of hydrous magnesium silicate, such asBen-A-Gel, using high shear agitation. This thickened water is addedwith high shear agitation until the silica concentration is 32%.

Then 18.7 lbs. of zinc dust is added to 7.42 lbs. of the binder to make1 gallon of paint.

The paint may be coated on the metal surface and allowed to dry at roomtemperature. The paint composition is stable and usable for up to 3weeks. The paint mixture when completed will contain 718% of pigment aszinc dust and 28.2% of binder. 'The binder is made up of 71.1% oforganic ammonium silicate containing 45 of SiO 5.9% of PbO, 0.46% ofhydrous magnesium silicate and 22.54% of water.

Final concentrations at 32% SiO and containing 0.32 to 0.66% ofBen-A-Gel gave satisfactory results as shown in the following tablewhere the percent of filler is based on the total weight of the binder.In this series two coats were applied to vertical metal strips withsimulated sand blasted surface:

gg g Zinc f Appearance 0 #1 0 Paint ran and saggod. 0.32 #1.. 400500Coating smooth, no runs or sags. 500-600 D0. 5004500 D0. 700-800 Coatingvery smooth, no

eieney.

runs or sags, very fine cracks at thick points.

Example 1 A series of coatings were prepared from organic ammoniumsilicates over a range of ratios of organic ammonium ion to silica. Ineach case 65 grams of zinc dust AA-1 was used with 20 ml. of the organicammonium silicate containing 32% of SiO;;:

8 at room temperature for one-half hour after which one panel was placedin a furnace at 500 C. for a half hour. After cooling, both coatingswere examined and tested OAS Cation Ratio S1011 Adheslm Water ResistanceStability of Percent gr. Paint, days 1 150 35 1 coat, 100; 2 coats, Canbe rubbed ofi 0. 68

2 0. easily. 2 1 22. 5 32 1 cztagt, 100; 2 coats, do 0.68 3 5 13. 05 321 coat, 300; 2 coats, CBHfiD-Ot be rubbed 2.

400. 0 4 220 12. 50 32 1 cggt, 400; 2 coats, do 1. 0

7 5 4 9. 69 32 1 c%at, 200; 2 coats, .do 1. 25 e 222 9. 54 32 OcJoat,300; 2 coats, .do 1. 5s 7 3 4. 48 32 1 coat, 100; 2 coats, Can be rubbedoff 1. 25

300. with hard rubbing. 8 610 1. 89 25 Coating does not dry out 1 Silicasol.

In this example no lead oxide was used. It is evident that the silicasol and the tetraethanolammonium silicate at the high ratio of 22.5 didnot form a satisfactory coating with the zinc. These systems containsilica almost entirely in the colloidal form. With a ratio of 4.48 thereis a high proportion of crystalloidal silica and at 1.89 the silica isalmost entirely crystalloidal. In the intervening ratios the proportionof crystalloidal to colloidal silica varies and apparently somecrystalloidal silica is necessary for satisfactory reaction with thezinc dust. No doubt, in the case of the most alkaline ratio, there wasnot suit]- cient zinc dust to react with the tetraethanolammoniumsilicate available.

Example 2 In this series of tests the paint systems were prepared as inExample 1 but included lead oxide. They were made with 65 grams of zincdust AA-l, ml. of the organic ammonium silicate containing 32% of Si0and 1.5 grams of PbO (18.5% based on the SiO;;):

for adhesion of the coating to the metal. The heated coating turned alittle darker gray. The non-heated coating could be scratched oil themetal with a normal weight of 300 g. using the Hoffman Scratch-HardnessTester whereas the heated coating could be scratched off only withdiificulty using a weight of 2000 grams. This high adhesion strengthdemonstrates the unusual suitability of the organic ammonium silicatesystems for painting surfaces which are exposed to high temperatures.

Example 4 Dry mixtures of organic ammonium silicate and metallic zincpowder are readily prepared. The organic ammonium silicate may be aspray dried powder or may be vacuum dried. In this example atetraethanolammonium silicate having a 10.0 ratio was vacuum dried andmixed with zinc powder. For the preparation of the coating system, waterwas added to give a concentration of 32% of SiO The mixture when firstwetted became very OAS SiO; PbO Water Resistance Stability No CationRatio (percent) (g.) Adhesion (after soaking 1 hour) oigaint,

ays

( 150 35 1. 5 Gelled on ball mill Could not be used 1 22.5 32 1.5 do 0 513.05 32 1.5 1 coat, 300; 2 coats, 600--.. Can be rubbed off very 7slightly with hard rubbing. 4 220 12. 5 32 1. 5 1 coat, 400; 2 coats,800--.. Cannot be rubbed ofi. 7 5 4 9. 69 32 1. 5 1 coat, 200; 2 coats,500--.- Can be rubbed 011 with 7 hard rubbing. 6 222 9. 54 32 1. 5 1coat, 400; 2 coats, 800--.- Cannot be rubbed ofl 7 7 3 .48 32 1. 5Gelled on ball mill Could not be used Adhesion measured in grams usingthe Hoffman Scratch-Hardness Tester. 2 Silica sol.

Example 3 In this example the paint was formulated with 2.0 ml. of #220organic ammonium silicate to which was added 1.5 grams of lead oxide, 3grams of talc and grams of zinc dust AA-l. The coatings were brushed onand dried thick and was diflicult to stir but as the silicate dissolved,in about 5 minutes, the paint thinned out and became normal. Panels werepainted and coatings tested for adhesion and water resistance. Adehydrated methyltriethanolammonium silicate at a 9.5 ratio was comparedin the same series of tests. These showed a little better adhesion thanthe tetraethanolammonium silicate binders but neither could be rubbedelf after soaking an hour in water. The dry mixtures were not found todeteriorate on standing.

Similarly, a series of tests were prepared in which lead oxide was alsoadded to the dry mixture of organic ammonium silicate and zinc. Thepaint system prepared by rliiiixing with water could be used for morethan one wee PAINTS PREPARED FROM MIXTURES OF ZINC DUST AND DRIED OASOAS Amt. oi Amt. of Amt. of Zine Water Resistance After Stabilit ofCation Silicate (g.) PbO (g.) Dust (g.) Water Adnesmn' soaking 1 hr.Paint, ays

11. 4 None 65 14.2 mls.2 costs, 500. Cannot be rubbed 011."- 1 11. 55None 65 14.0 mls.-1 coat, 300; 2 o 1 coats, 600. 11. 55 1. 5 65 14.0mls.-1 coat, 200; 2 .do 7

coats, 500. 11. 4 1. 5 65 Can be rubbed 011E 7 coats, 500

9 Example Zinc-rich coatings may be top coated, if desired. This may bedone for the sake of appearance or to prevent attack from water andindustrial fumes. The top coating may be an organic ammonium silicatepigment paint of our parent application or a paint with an organicbinder, or both. The coatings with organic ammonium silicate binders arereadily compatible. With the organic top coats, the best adhesion isobtained with vinyl, epoxy, or butadiene systems, and in some casesadhesion of the organic base paint is increased by washing andweathering the organic ammonium silicate base coat.

In some field experiments a gray OAS pigmented paint having thefollowing formulation:

Organic ammonium silicate 220 (32% SiO ml 1000 PhD ground into thesilicate with a ball was used to top-coat zinc-rich OAS coatings. Thesecoatings have not shown any effect of weathering after eight monthsexposure. A commercial marine paint has been applied as a top coatingfor OAS zinc-rich coatings. It was found that after weathering for onemonth small blisters appeared unless the panel was first washed. Aseries of panels were exposed to the weather, facing east at a 45 slant.The panel coated only with one coat of the above gray pigment paintbegan to rust after the first rain and was completely covered with rustafter 3 months exposure. Other panels, coated either with two coats ofthe zinc-rich paint or with one coat of zinc-rich paint and one finishcoat of the above gray pigment paint, still showed no rust after 8months.

Example 6 The metal surface of an industrial spray dryer used over atemperature cycle was wire brushed leaving a fine layer of loose rust. Acoating of the zinc-rich paint of Example 3 was applied to one sectionby a brush. Another section was coated with the gray pigment paint ofExample 5, and a further section was first coated with the zincrichcoating and then with the gray pigment paint. A section of aluminumexhaust pipe was painted in the same manner. After 7 months the paint onthe aluminum exhaust pipe was in perfect condition; the paint on thesteel surface of the dryer was also in perfect condition except for afew spots in the section painted only with the gray pigment paint.

Example 7 Areas on a hot boiler stack were sand blasted free of rust. Acoating of zinc-rich paint described below Was applied to this hotsurface. The water boiled off leaving a rough and uneven surface sincethe surface temperature was 250300 F. A similar section was coated withthe gray pigment paint of Example 5.

Another area on the blow-out tank of the boiler was cleaned With a wirebrush which removed most of the old paint. One area was painted with thezinc-rich paint described below; another with the gray pigment paint ofExample 5; and a third was painted first with the zincrich paint andtop-coated with the pigment paint. This blow-out tank was cold at thetime of application and a good, even film was formed. The metal washeated several times a day but not to as high a temperature as thestack. After 6 months there was no evidence of rust on the areas of thestack painted with either the zinc-rich paint or the gray pigment paint.However, on the blow-out tank the area painted with pigment paint hadlarge rust spots whereas the areas first coated with the zinc-rich paintshowed no rust at all. Other paints crack and peel off the blow-out tankbecause of the rapid expansion during heating and cooling.

Lead oxide ground into the organic ammonium silicate, and the residueremoved with a centrifuge 18.5

This made 840 parts by weight of binder which was mixed with 2,125 partsby wegiht of zinc dust (Asarco #1).

Example 8 A manifold on an automobile engine was coated by brushing on azinc-rich organic ammonium silicate paint having the formulation:

#220 organic ammonium silicate (32% SiO ml 20 PhD g 1.5 Zn metal powderg 65 The metal was not prepared in any way. After 20,000 miles and ahard winter the coating was still in perfect condition and was unchangedin appearance. Water, snow and salt splashing up on the hot manifold hadno effect on the coating.

More or less detailed claims Will be presented hereinafter, and eventhough such claims are rather specific in nature those skilled in theart to which this invention pertains will recognize that there areobvious equivalents for the specific materials recited therein. Some ofthese obvious equivalents are disclosed herein, other obviousequivalents will immediately occur to one skilled in the art, and stillother obvious equivalents could be readily ascertained upon rathersimple, routine non-inventive experimentation. Certainly no inventionwould be involved in substituting one or more of such obviousequivalents for the materials specifically recited in the claims. It isintended that all such obvious equivalents be encompassed within thescope of this invention and patent grant in accordance with thewell-known doctrine of equivalents as well as changed proportions of theingredients which do not render the composition unsuitable for thedisclosed purposes. Therefore, this application for Letters Patent isintended to cover all such modifications, changes and substitutions aswould reasonably fall within the scope of the appended claims.

What is claimed is:

1. A corrosion resistant coating composition for metal consistingessentially of:

(a) an aqueous solution of an organic ammonium silicate which ischaracterized by the formula X N R 0 YSiO -ZH O wherein:

N represents a nitrogen atom; n is a small integer less than 10 andpreferably less than 5; X, Y, and Z represent numbers defining therelative amounts of each of the component parts of the compound, andmore specifically, X is 1, Y is preferably between 0.5 and 50, and Z ispreferably between 0 and 99; R represents alkyl radicals containingbetween 1 and 20 carbon atoms, at least one of which is an omega hydroxyalkyl group; up to four R groups being associated with each N;

p is at least 4, indicating total bonds of R groups to N; and

s is an integer from 1 to p, indicating the number of different types ofR groups,

(b) a finely divided zinc powder in the amount of between about 6 to 20grams of zinc powder per gram of SiO 2. A coating composition accordingto claim 1 which additionally contains hydrous magnesium silicate.

3. A coating composition according to claim 1 which 1 1 additionallycontains a finely divided lead oxide and a filler.

4. The process of preparing a corrosion resistant coating which consistsessentially of:

(a) bringing together an organic ammonium silicate of the type set forthin claim 1 and a filler suspended in water,

(b) admixing the components set forth in (a) using shear agitation, and

(c) thereafter adding a finely divided powdered zinc in the amount ofbetween about 6 to 20 grams of zinc powder per gram of SiO;.

5. The process of forming the composition of claim 3 which comprisesmilling lead oxide into said organic ammonium silicate solution untilcompletely dispersed said dispersion of lead oxide in organic ammoniumsilicate being thickened by adding a water suspension of hydrousmagnesium silicate and finely divided zinc powder.

6. A dry mixture comprising a powdered organic ammonium silicate asdefined in claim 1 and powdered zinc pigment dispersible in water forcoating on metal, said zinc powder being in an amount of between about 6and 20 grams of Zinc powder per gram of SiO References Cited UNITEDSTATES PATENTS 3,056,684 10/1962 Lopata et a1. 1 06.1 X 3,202,517 8/1965Jarboe et a1. 106l4 2,689,245 9/ 1954 Merrill.

2,944,919 7/1960 Morris et al. 7

2,998,328 8/1961 Munger et a1. 117--705 3,100,154 8/1963 Oshima et al.

3,248,237 4/1966 Weldes et al. l0638.35.

g0 ALEXANDER H. BRODMERKEL, Primary Examiner.

DONALD J. ARNOLD, Examiner. L. B. HAYES, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,372,038 March 5 1968 Helmut Hans Wilhelm Weldes et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 38, "siilcate" should read silicate line 60, "providers"should read powders Column 4, line 12, "rubber" should read rubbedColumns 7 and 8, in the second TABLE, sixth column, in the heading,"Adhesion" should read Adhesion Column 11, line 15, after "dispersed"insert a comma. Column 12 line 8 "triethyla mmonium silicate" shouldread triethanolammonium silicate Signed and sealed this 23rd day ofSeptember 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. A CORROSION RESISTANT COATING COMPOSITION FOR METAL CONSISTINGESSENTIALLY OF: (A) AN AQUEOUS SOLUTION OF AN ORGANIC AMMONIUM SILICATEWHICH IS CHARACTERIZED BY THE FORMULA